How Water Is Cracking Up Antarctica

Jan. 17

By Lee Dye

A chunk of ice the size of Connecticut that had hovered along the coast of Antarctica for hundreds of years has disintegrated in less than a decade, and scientists believe they have finally figured out why.

If they are right, it took only a slight increase in summertime temperatures to spell the doom for the Larsen Ice Shelf.

Much attention has been focused on the ice shelf since it began dramatically breaking up in 1995, and it appears that the driving force that ripped it apart was simply water.

A team of scientists led by Ted Scambos of the University of Colorado at Boulder used satellite images, a NASA computer and historical records to conclude that many other areas of Antarctica could face a similar future. It is a matter of great concern because massive melting of the glaciers at the bottom of the world could cause the seas to rise globally, inundating low-lying areas.

Small Warming Means Big Melting

What's troubling about the scientists' report, published in the January issue of the Journal of Glaciology, is it didn't take much to trigger the process that virtually destroyed the Larsen Ice Shelf.

"What we saw was an indication that climate doesn't have to change a whole lot to have a much more rapid effect than was previously thought," says Scambos.

He insists, however, that he's no prophet of doom. It would take decades, if not centuries, to melt Antarctica's glaciers, he says. But the team's research suggests that the beginning of the process could come sooner than most scientists had thought.

One reason many scientists have doubted the doomsday scenario for Antarctica is the mean annual temperature there has remained fairly constant over the years. Some areas have experienced a rise of a few degrees over the last 50 years, but many experts believed that the temperature would probably have to rise about 20 degrees to make much difference.

But Scambos and his team found that the average annual temperature is not nearly as important as seasonal changes. A warmer summer can cause a dramatic change, even if the overall temperature for the year remains fairly constant.

That, apparently, is what happened on the Antarctic Peninsula, a long finger of land that points toward South America. The summertime temperature there has been two or three degrees warmer in recent years, playing havoc with the Larsen Ice Shelf along its shoreline.

Water in the Cracks

The warmer temperature caused some surface melting during the summer, the researchers say, and that caused cracks in the ice to fill with water.

Since water is denser than ice, it caused pressure to build within the crack, forcing the ice to break further, Scambos says.

Team member Christine Hulbe of NASA's Goddard Space Flight Center in Greenbelt, Md., used a NASA computer to measure the impact of water in a surface crack. The computer model revealed an astonishing fact. If the crack was only 15 feet deep, Hulbe found, the water would force its way down, propagating the crack all the way through a sheet of ice more than 600 feet thick.

That process apparently left the Larsen in tatters, held together here and there by narrow bands of ice that bridged across two sections of the shelf. When the bridges broke, like during a storm, a giant iceberg was released into the sea.